The traditional monopolies of electrical utility companies have been relaxed in the past few years in the European Union, in the United States and in other countries. There has developed as a result a growing wholesale electricity supply market for electrical power. Utility companies, independent power producers, and power marketers as well as brokers are some of the participants in the volatile electricity supply market. It is known, for example, that variables such as the time of day and date, weather, temperature and oil prices play a role in the pricing of electricity in a given region. Similarly the way in which the electrical power transmission line (or power grid) and the pricing of electricity play a role for in the storage of fuel, such as oil, and other commodities.
Furthermore, the pricing of the electricity is dependent on the operational status of electricity supply generators and use of facilities as well as the transmission capacity of an electric power transmission network (also called a power grid). The participants in the electricity supply markets require access to substantially real-time information as well as historical data on the operational status of the electricity supply generation and use facilities as well as the electric power transmission lines in the region. This information allows the development of trading strategies in electric power and responses to power system events (such as disruptions in the power grid due to failures of transformers).
The relaxation of the monopoly status of traditional electric utility companies has resulted in increased competition for customers among suppliers of electric power. Information relating to the use of electric power by the potential customers would be useful to those involved in the bidding for electrical supply contracts. It would also be advantageous to determine information on the supply and the demand of the electric power over time without having to directly connect to the electrical power transmission lines.
There is also a requirement to monitor the power grid in order to ensure an increasing stability of the power grid. The power grid increase in size and complexity. This, in addition to faster trading of power (US), increases the need for fast and more direct measurement of the grid conditions to be able to adjust these grid conditions within the time frames needed to avoid an oscillating system.
One of the issues related to the relaxation of the monopoly status of traditional electric utilities is the requirement to determine power system disturbances in the power grid. U.S. Pat. No. 7,519,454 (Gardner et al., assigned to Virginia Tech Intellectual Properties) teaches a system for detecting and locating the disturbance events within the power grid. The system includes a series of frequency disturbance recorders taking measures in the power grid at disparate points of the power grid and an information management system, which is configured to receive data from the series of the recorders and to analyse the received data. The frequency data recorders include a low pass filter to eliminate high frequency components in a measured 110V AC signal from an outlet socket located in an office or in a home. The system of U.S. '454 further includes a communications network interconnecting the series of frequency data recorders and the information management system. The information management system is configured to examine orders and patterns of receipt of the frequency changes caused by the disturbance event and to triangulate a location of the disturbance event based on the orders and patterns of receipt of the frequency changes. The teachings of the U.S. '454 patent require the measurement of a complete cycle of the frequency to determine a change in the frequency and also lose information by eliminating the high frequencies in the 110V AC signal.
Methods and systems for the measurement for the electric power transmission are known from several prior art documents. For example U.S. Pat. No. 6,714,000 (Staats, assigned to Genscape, Inc.) teaches a method for the remote monitoring of the magnitude and the direction of net electrical power and current flow to or from a facility monitored over a prolonged period of time. The method described in the Staats U.S. '000 Patent includes the detection and the measurement of the magnetic field emanating from the monitored electrical power transmission lines and detecting a signal that is synchronized to the power system frequency emanating from the power lines. The method further includes evaluation, storing and transmission of the data on the electromagnetic field that emanates from the electrical power transmission line.
A further International Patent Application No. WO2006/112839 (Genscape Intangible Holding, Inc.) also teaches a method and a system for the substantially real-time monitoring of the operational dynamics of power plants and other components in an AC power grid. The monitoring is done by using information collected from a network of power grid frequency detection and reporting devices. The invention allows for the real-time detection and reporting of certain power grid events, such as a power plant trips or failures.
International Patent Application No. WO2007/030121 (Genscape Intangible Holding, Inc.) teaches a system for monitoring the power flow along an electric power transmission line that includes a plurality of magnetic field monitors placed at selected positions. The magnetic field monitors have two magnetometers with their sensitive axis placed either in the horizontal or vertical direction. A detailed description of such magnetic field monitors is found in U.S. Pat. No. 6,771,058 (Lapinski). The system further includes a central processing facility for the communication of the power flow to an end user.
European Patent No. EP1 297 347 (Genscape Intangible Holding, Inc.) discloses an apparatus for remotely measuring and monitoring an electric power transmission line. The apparatus comprises a first sensor which is responsive to a first component of a magnetic flux density associated with the electric power transmission lines and which outputs a volt proportional to the magnetic flux density generated by current flowing through set electrical power transmission line. The apparatus further includes a second sensor, which outputs a voltage proportional to a net electrical potential associated with the electrical power transmission line. The values for the voltage and the current flowing through the electrical power transmission line are passed to a central processing facility which combines the phase of the measured electrical potential with the phase of the measured magnetic flux density in order to determine the phase of the electrical potential relative to the magnetic flux density and that by determining from the face of the electrical potential relative to the magnetic flux density. The phase angle of the current flowing through the electrical power transmission line with respect to the voltage of the transmission line is also determined. A power factor on the electric power transmission line and the magnitude and the direction of the power flowing through the electrical power transmission line is thereby calculated. It should be noted that the voltage sensor and the magnetic flux sensor are substantially co-located, as can be seen from FIG. 1 of the patent.
Other companies also measure power flowing along electric power transmission lines. For example, the Norwegian company powermonitor.org supplies information about the German power plants. Their product is described in the article “Slik drives strøm-spionasje”, Økonomisk Rapport April 2006, 40-41. Another Norwegian Company, Energieinfo A S, Stavern, has filed a Norwegian patent Application entitled “Fremgangsmåte og apparat for overvåkning av produksjon og overføring av elektrisk kraft” (Application No. NO 2007 2653).
International patent application No. WO 2013/135773 A1 discloses also an apparatus and a method for monitoring power transmission, disturbances and forecasts in a power grid. The apparatus comprises a plurality of magnetic field sensors or voltage sensors for measuring a change in the magnetic field or voltage over time at the electric power transmission line. The measurements are mainly based on signals from magnetic field sensors, which are prone to interferences.
In the international patent application No. WO 2013/001355 A2 a method for distributed waveform recording in a power distribution system is disclosed. The purpose of the method is fault monitoring and analysis of fault conditions condition in the power distribution system. The method includes one or more instrument transformers along with merging units and a plurality of intelligent electronic devices distributed in a plurality of hierarchical levels. The distributed waveform recording is carried out by at least two devices participating to detect an event for recording and performing waveform recording, where the data for waveform recording and detection of event are based on a single stream of the sampled measured value data.
From international patent application No. No. WO 2007/070255 A2 a system for detecting and locating a disturbance event within a power grid is known. The system includes a series of frequency disturbance recorders taking measurements in the power grid at dispersed points of the power grid, an information management system, configured to receive data from the serious of frequency disturbance recorders and analyze the received data and a communications network interconnecting the series of frequency disturbance recorders and the information management system. The disclosed system is not suitable for retrieving information about the power grid in a regular state as for example power flow.
US patent application No. US 2013/0073108 A1 discloses a real time distributed wide area monitoring system. The system includes a plurality of phasor measurement units that measure respective synchronized phasor data of voltages and currents. The real time distributed wide area monitoring system further includes a plurality of processing subsystems distributed in a power system. At least one of the processing subsystems is configured to receive a subset of the respective synchronized phasor data and to process the received subset of the respective synchronized phasor data to determine respective system parameters.
In US patent application No. US 2012/0310559 A1 a system for distributed data collection in a utility grid is disclosed. The system provides distributed data collection for sensor networks in a utility grid and comprises one or more data collection agents, one or more grid data collection service devices, and one or more points of use. The data collection agents may be configured to generate grid data values that comprise raw grid data values, processed grid data values, or any combination thereof. The data collection agents may also be configured to communicate the grid data values using a communication network in the utility grid to the one or more grid data collection service devices. The grid data collection service devices receive the grid data values in a time synchronized manner and distribute the time synchronized grid data values in substantially real time to the one or more points of use.
A method and apparatus for time synchronization and measurement of power distribution systems is known from US patent application No. US 2011/0208364 A1. The method includes receiving a synchronized wireless communication signal, synchronizing to the synchronized wireless communication signal to produce synchronized time, performing one or more power distribution measurements based on the synchronized time to produce synchronized power distribution measurements, and transmitting the synchronized power distribution measurements to a power control center. The apparatus includes a receiver configured to receive a synchronized wireless communication signal, a measurement module configured to perform power distribution measurements based on the synchronized time, and a transmitter configured to transmit synchronized power distribution measurements to a power control center.
US patent application No. US 2011/0010118 A1 discloses a method and an apparatus for monitoring power transmission in an electric power transmission line. The apparatus comprises a magnetic field sensor for measuring the magnetic field at the electric power transmission line and transmitting magnetic field data to a processor. The apparatus also has a voltage sensor arranged distally from the magnetic field sensor for transmitting voltage waveform data to the processor and a transfer function calculator for calculating the relationship between the transmitted voltage waveform data at the voltage sensor and transmission line voltage waveform data.
From US patent application No. US 2009/0289637 A1 a system and a method for determining the impedance of a medium voltage power line is known. The system and method uses a computer system to provide utility information related to a plurality of underground power line cable segments connected on opposite ends to different distribution transformers. The method comprises monitoring the impedance of underground power line cable segments overtime, detecting a change in the impedance, storing information for identifying power line cable segments, generating a report that identifies the set of the plurality of underground power line cable segments for which a change in impedance is detected, and outputting the report.
Real time power line sag monitoring using time synchronized power system measurements is disclosed in US patent application No. US 2008/0189061 A1. The disclosed system includes a sag calculator, which computes sag for a span of a line section based, at least in part, upon an average temperature of the conductors in the line section. The system also includes a temperature calculator, which determines the temperature and which uses time synchronized power system voltage and current measurements. The voltage and current measurements are generated for example by phasor measurement units.
US patent application No. US 2008/0077336 A1 discloses a power line universal monitor sensor module for measuring global positioning satellite synchronized voltage, current, phase, frequency and derived quantities on the AC power conductor. The disclosed sensor is suitable for installation on and removal from the energized high voltage AC power conductor.
A system and method of monitoring a plurality of electrical assets is disclosed in US patent application No. US 2007/0059986 A1. The system comprises an electricity distribution infrastructure, including a plurality of electrical asset sensors coupled to the electrical assets for monitoring an operating condition of the electrical assets as well as any fault conditions. The sensors may include a current transformer, a GPS receiver for applying a synchronized time stamp to waveform data, and a mesh network radio for transmitting the time stamped waveform data.
From US patent application No. US 2006/0247874 A1 a system and method for synchronized phasor measurement is known. The phasor measurement system includes acquisition circuitry for acquiring voltage or current values from a power line, sampling circuitry for sampling the voltage or current values, and processing circuitry for computing a phasor and at least one time derivative of the phasor based on the sampled voltage or current values and for computing a synchronized phasor value based on the phasor and the at least one time derivative of the phasor.
The prior art systems described in these publications are, for example, expensive due to need of placement of equipment out in the field near to the power lines or insufficient speed in making the measurements, or lack information as to the power flow and direction. The prior art methods are under-determined for the measurement and calculation of power grid parameters and will not work if less than three recorders are used.